Hot-pressing apparatus

ABSTRACT

This invention relates to a hot-pressing method and a hot-pressing apparatus capable of quenching a workpiece at a sufficient cooling rate. In a hot-pressing step, a hot-pressing apparatus presses and cools a workpiece at the same time. The hot-pressing apparatus includes a lower die and an upper die whose forming surfaces face each other. A top surface of the lower die is provided with a plurality of beads so that a part of the workpiece difficult to come in contact with the forming surface of the lower die and the forming surface of the upper die positioned at the bottom dead center is formed into a stepped shape.

TECHNICAL FIELD

The present invention relates to a hot-pressing method and a hot-pressing apparatus for pressing and cooling a heated workpiece at the same time.

BACKGROUND ART

Conventionally, a hot-press forming is widely known in which a pressing machine to which a pair of dies (an upper die and a lower die) are attached presses a workpiece, such as a steel plate, heated to above a temperature at which an austenite structure appears, and at the same time, brings the dies into contact with the workpiece to quench the workpiece.

A technique on the hot-press forming is publicly known which enables the dies to suitably cool the workpiece during the quenching by forming water channels through which cooling water flows inside the dies to cool the dies (for example, see Patent Literature 1).

However, when the workpiece is quenched, clearances are formed between the workpiece and the dies because of variation in the thickness of the workpiece caused by the press working, a precision error in the forming surfaces of the dies caused when the dies are manufactured, flexure of the dies during the press working, and the like. Consequently, a part of the workpiece where the clearance between the part and the dies is larger than a predetermined size has decreased contact areas with the forming surfaces of the dies when the workpiece is quenched, which causes a problem that the part is cooled at an insufficient cooling rate, and hardness of the part is smaller than a predetermined value,

For example, as shown in FIG. 8, in the case where a flat plate-like workpiece W is formed into what is called a hat shape, large clearances tend to form between a top part Wt situated in the uppermost part of the pressed workpiece W, and the dies. Therefore, it is probable that hardness of the top part Wt is smaller than a predetermined value.

CITATION LIST Patent Literature

Patent Literature 1: JP 2005-7442 A

SUMMARY OF INVENTION Problem to Be Solved By the Invention

The objective of the present invention is to provide a hot-pressing method and a hot-pressing apparatus capable of quenching a workpiece at a sufficient cooling rate.

Means for Solving the Problem

A first aspect of the invention is a hot-pressing method for pressing and cooling a heated workpiece at the same time, using a lower die having a lower forming surface, and an upper die having an upper forming surface facing the lower forming surface. The hot-pressing method includes a step for pressing the workpiece so as to form a part of the workpiece difficult to come in contact with the lower forming surface of the lower die and the upper forming surface of the upper die positioned at a bottom dead center into a stepped shape.

A second aspect of the invention is a hot-pressing apparatus including a lower die having a lower forming surface, and an upper die having an upper forming surface facing the lower forming surface, which causes the lower die and the upper die to press a heated workpiece arranged therebetween, and at the same time, to keep the forming surfaces thereof in contact with a surface of the workpiece to cool the workpiece. In the hot-pressing apparatus, at least one of the forming surfaces of the lower die and the upper die is formed as a bumpy surface so that a part of the workpiece difficult to come in contact with the lower forming surface of the lower die and the upper forming surface of the upper die positioned at a bottom dead center is formed in a stepped shape.

Preferably, one of the lower die and the upper die has a protrusion which protrudes from an intermediate part, in a right-left direction, of the forming surface thereof toward the forming surface of the other, and which is continuously formed in a front-rear direction perpendicular to the right-left direction. The other of the lower die and the upper die has a recess which is recessed from an intermediate part, in the right-left direction, of the forming surface thereof in conformity with a shape of the protrusion, and which is continuously formed in the front-rear direction. The forming surface on which the protrusion is formed includes a top surface extending in the right-left direction at a protruding end of the protrusion, two lateral surfaces extending in a direction opposite to that in which the protrusion protrudes from both ends of the top surface in the right-left direction, and two base surfaces extending outward in the right-left direction from extending ends of the lateral surfaces. The top surface is formed as the bumpy surface.

Effects of the Invention

The present invention makes it possible to quench a workpiece at a sufficient cooling rate, and to prevent hardness of some parts in the workpiece from being smaller than a predetermined value.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a hot-pressing apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing beads.

FIG. 3 illustrates the hot-pressing apparatus in which an upper die is at the bottom dead center.

FIG. 4 illustrates beads which are formed so that the forming surfaces of dies are recessed.

FIG. 5 shows a workpiece being pressed.

FIG. 6 is a perspective view showing another embodiment of beads.

FIG. 7 is a perspective view showing another embodiment of beads.

FIG. 8 illustrates a conventional hot-pressing apparatus.

DESCRIPTION OF EMBODIMENTS

With reference to FIGS. 1 and 2, described below is a hot-pressing apparatus 1 as an embodiment of a hot-pressing apparatus according to the present invention.

The hot-pressing apparatus 1 performs hot-press forming of a workpiece W.

The workpiece W is a steel plate to be worked by the hot-pressing apparatus 1, and is heated to above a temperature at which an austenite structure appears by ohmic heating and the like.

For convenience, a top-bottom direction in FIG. 1 is defined as a top-bottom direction of the hot-pressing apparatus 1, and a right-left direction in FIG. 1 is defined as a right-left direction of the hot-pressing apparatus 1. In addition, this side in FIG. 1 is defined as a front side of the hot-pressing apparatus 1, and the far side in FIG. 1 is defined as a rear side of the hot-pressing apparatus 1, thereby a front-rear direction of the hot-pressing apparatus 1 being defined.

As shown in FIG. 1, the hot-pressing apparatus 1 includes a lower die 10 and an upper die 20 whose forming surfaces face each other.

The lower die 10 corresponds to the upper die 20. The lower die 10 is produced by performing numerical control machining of a predetermined ingot. The lower die 10 is configured so that cooling water flows thereinside.

The lower die 10 has a protrusion 11 which protrudes upward from the forming surface (the upper surface) thereof.

The protrusion 11 protrudes upward from the forming surface of the lower die 10. The protrusion 11 is continuously formed in the front-rear direction in the intermediate part (the substantially middle part), in the right-left direction, of the forming surface of the lower die 10.

The lower die 10 has a top surface 10 a extending in the right-left direction at the protruding end (uppermost part) of the protrusion 11, two lateral surfaces 10 b extending in a direction opposite to that in which the protrusion 11 protrudes (in the bottom direction) from both the ends of the top surface 10 a in the right-left direction, and two base surfaces 10 c extending outward in the right-left direction from the extending ends (the bottom ends) of the lateral surfaces 10 b. These surfaces act as what is called a hat-shaped forming surface of the lower die 10.

The top surface 10 a of the lower die 10 is provided with a plurality of beads 12.

As shown in FIG. 2, the bead 12 protrudes upward from the top surface 10 a. The bead 12 has a shape in which a semicircular section thereof whose arc is situated at the upper part thereof continues in the front-rear direction from the vicinity of the front end to the vicinity of the rear end of the protrusion 11. In other words, the bead 12 has a shape similar to that of one of two equal parts into which a cylinder with an axis parallel to the front-rear direction is divided along the axis, and is arranged so that the flat surface (cutting surface of one of two equal parts into which a cylinder is divided) comes in contact with the top surface 10 a.

The plurality of beads 12 (in the present embodiment, three beads 12) are arranged at predetermined intervals in the right-left direction.

The bead 12 is made of the same metal as the lower die 10, or a metal with hardness larger than that of the lower die 10. The bead 12 is formed by, after performing buildup welding on the top surface 10 a, performing numerical control machining so that the buildup part is formed into a predetermined shape, by performing numerical control machining so that the top surface 10 a is formed into a predetermined shape when producing the lower die 10 from a predetermined ingot, or by means of a similar technique.

Thus, the bead 12 is formed in order to change the top surface 10 a of the lower die 10 into a bumpy surface.

As shown in FIG. 1, the upper die 20 corresponds to the lower die 10. The upper die 20 is produced by performing numerical control machining of a predetermined ingot. The upper die 20 is configured so that cooling water flows thereinside.

The upper die 20 has a recess 21 recessed upward from the forming surface (the lower surface) of the upper die 20 in conformity with the shape of the protrusion 11.

The recess 21 is formed so that the forming surface of the upper die 20 is recessed upward. The recess 21 is continuously formed in the front-rear direction in the intermediate part (the substantially middle part), in the right-left direction, of the forming surface of the upper die 20.

The upper die 20 has a bottom surface 20 a extending in the right-left direction at the innermost part (uppermost part) of the recess 21, two lateral surfaces 20 b extending in a direction opposite to that in which the recess 21 is recessed (in the bottom direction) from both the ends of the bottom surface 20 a in the right-left direction, and two base surfaces 20 c extending outward in the right-left direction from the extending ends (the bottom ends) of the lateral surfaces 20 b. These surfaces act as what is called a hat-shaped forming surface of the upper die 20.

The hot-pressing apparatus 1 configured as mentioned above causes the lower die 10 and the upper die 20 to press the heated plate-like workpiece W arranged between the forming surfaces thereof to form the workpiece W into what is called a hat shape by moving the upper die 20 to the bottom dead center so that the upper die 20 cones close to the lower die 10. At the same time, the hot-pressing apparatus 1 causes the lower die 10 and the upper die 20 to keep the forming surfaces thereof in contact with the surface of the workpiece W to cool the workpiece W. Consequently, the hot-pressing apparatus 1 produces the workpiece W as a product.

With reference to FIGS. 3 to 7, described below is a hot-pressing step S1 as an embodiment of a hot-pressing method according to the present invention.

The hot-pressing step S1 is a step in which the hot-pressing apparatus 1 performing the hot-press forming of the workpiece W.

In the hot-pressing step S1, by moving the upper die 20 to the bottom dead center so that the upper die 20 comes close to the lower die 10, the hot-pressing apparatus 1 causes the lower die 10 and the upper die 20 to press the heated plate-like workpiece W arranged between the forming surfaces thereof, and at the same time, brings the lower die 10 and the upper die 20 into contact with the workpiece W to quench the workpiece W.

As shown in FIG. 3, since the top surface 10 a of the lower die 10 is provided with the plurality of beads 12, a top part Wt (a part corresponding to the top surface 10 a) situated in the uppermost part of the pressed workpiece W is formed into a stepped shape along the shapes of the plurality of beads 12 when the workpiece W is pressed in the hot-pressing step S1. In other words, the plurality of beads 12 act as a means which changes the top surface 10 a into a bumpy surface to form a part of the workpiece W into the stepped shape.

Note that the “stepped shape” of the workpiece W is a shape in which the workpiece W is bent to protrude toward the forming surfaces of the lower die 10 and the upper die 20. In the present embodiment, the workpiece W is formed into the wavy stepped shape in which two parts protruding toward the forming surface (the top surface 10 a) of the lower die 10 are formed, and three parts protruding toward the forming surface (the bottom surface 20 a) of the upper die 20 are formed.

Since the top part Wt of the workpiece W is formed to protrude toward the forming surfaces of the lower die 10 and the upper die 20, compared with the case where the top part Wt is not formed in the stepped shape, the top part Wt has large contact areas with a part of the forming surface of the lower die 10 where the plurality of beads 12 are not formed, and the forming surface of the upper die 20 when the workpiece W is quenched in the hot-pressing step S1.

Moreover, since the top part Wt of the workpiece W is formed along the shapes of the plurality of beads 12 formed on the top surface 10 a of the lower die 10, the top part Wt comes in contact with the plurality of beads 12 forming a part of the forming surface of the lower die 10 along the shapes of the plurality of beads 12 when the workpiece W is quenched in the hot-pressing step S1. Thereby, compared with the case where the plurality of beads 12 are not formed on the top surface 10 a of the lower die 10, the top part Wt has large contact area with the forming surface of the lower die 10.

These make it possible, when the workpiece W is quenched in the hot-pressing step S1, to cool the top part Wt of the workpiece W at a sufficient cooling rate, and to prevent hardness of the top part Wt from being smaller than a predetermined value.

In the present embodiment, the top surface 10 a of the lower die 10 is provided with the plurality of beads 12 so that the top part Wt of the workpiece W is formed into the stepped shape.

This is because, when the workpiece W formed in the hat shape is quenched, large clearances tend to form between the top part Wt of the workpiece W and the dies (see FIG. 8), and hardness of the top part Wt is more likely to be smaller than a predetermined value.

In other words, the top surface 10 a of the lower die 10 is provided with the plurality of beads 12 so that a part of the workpiece W difficult to come in contact with the forming surfaces of the lower die 10 and the upper die 20 positioned at the bottom dead center is formed into the stepped shape.

Note that the “part difficult to come in contact” with the forming surfaces of the lower die 10 and the upper die 20 positioned at the bottom dead center in the workpiece W is a part where an amount of clearance (a distance) between the workpiece W and conventional dies which does not have the plurality of beads 12 is larger than a predetermined value when the workpiece W is quenched, namely, a part where hardness thereof is smaller than a predetermined value (is insufficient) after the hot-press forming. The part is may previously be found by a simulation and the like.

As mentioned above, the top surface 10 a of the lower die 10 is provided with the plurality of beads 12, thus enabling to form the top part Wt difficult to come in contact with the forming surfaces of the lower die 10 and the upper die 20 positioned at the bottom dead center into the stepped shape.

Therefore, it is possible to increase the contact areas between the top part Wt of the workpiece W, and the forming surfaces of the lower die 10 and the upper die 20 to prevent the hardness of the top part Wt from decreasing, and to secure suitable hardness in the whole workpiece W.

Consequently, it is possible to do away with the need to remake the dies so that the dies suitably come in contact with the workpiece W, and to reduce man-hour required to produce the dies. In addition, it is possible to reduce the time required to quench the workpiece W owing to increased contact areas between the workpiece W and the forming surfaces of the dies, and consequently to increase speed for producing a product.

In the present embodiment, only the top surface 10 a of the lower die 10 is provided with the plurality of beads 12, but the configurations of the dies are limited thereto as long as the top part Wt is formed into the stepped shape.

For example, a plurality of beads similar to the plurality of beads 12 may be provided to the bottom surface 20 a of the upper die 20 in addition to the plurality of beads 12 provided to the top surface 10 a of the lower die 10, or the plurality of beads similar to the plurality of beads 12 may be provided to only the bottom surface 20 a of the upper die 20.

As shown in FIG. 4, a plurality of beads 112 and a plurality of beads 122 which do not protrude from the forming surfaces of the dies as the plurality of beads 12 but are recessed from the forming surfaces of the dies may be provided to the lower die 10 and the upper die 20, respectively.

The bead 112 is formed on the top surface 10 a of the lower die 10 so that a semicircular section thereof whose are is situated at the lower part thereof continues in the front-rear direction, and two beads 112 are arranged at a predetermined interval in the right-left direction. The bead 112 is formed in order to change the top surface 10 a of the lower die 10 into a bumpy surface.

The bead 122 is formed on the bottom surface 20 a of the upper die 20 so that a semicircular section thereof whose arc is situated at the upper part thereof continues in the front-rear direction, and three beads 122 are arranged at predetermined intervals in the right-left direction. The bead 122 is formed in order to change the bottom surface 20 a of the upper die 20 into a bumpy surface.

The bead 112 and the bead 122 are alternately arranged at different positions in the right-left direction.

Note that beads such as the bead 112 and the bead 122 may be formed by performing numerical control machining to cut the forming surfaces of the dies.

In the present embodiment, the dies have the shapes to form the top part Wt of the workpiece W into the stepped shape. However, in the case where parts of the workpiece W other than the top part Wt are difficult to come in contact with the forming surfaces of the lower die 10 and the upper die 20 positioned at the bottom dead center, the dies should be formed in the shapes to form the parts of the workpiece W other than the top part Wt into the stepped shape. For example, a plurality of beads should be formed on the base surfaces 10 c of the lower die 10.

In the present embodiment, the plurality of beads 12 are formed on the top surface 10 a which is the surface of the lower die 10 situated in the uppermost part thereof.

As shown in FIG. 5, in the hot-pressing apparatus 1 configured to move the upper die 20 to the bottom dead center, the top surface 10 a which is the surface of the lower die 10 situated in the uppermost part thereof comes in contact with the workpiece W at a relatively early stage when the workpiece W is pressed. In other words, the part to be finally formed into the top part Wt is worked at a relatively early stage.

Thereby, when the upper die 20 arrives at the vicinity of the bottom dead center (for example, 1 mm above the bottom dead center), the top part Wt of the workpiece W is formed into the stepped shape. In other words, the plurality of beads 12 are arranged at such positions that the top part Wt of the workpiece W is formed into the stepped shape when the upper die 20 arrives at the vicinity of the bottom dead center.

This makes it possible to increase the contact area between the top part Wt of the workpiece W and the forming surface of the lower die 10 from a stage where the workpiece W is being pressed, and to further prevent the hardness of the top part Wt from decreasing.

In the present embodiment, three beads 12 each of which has the shape similar to that of one of two equal parts into which a cylinder is divided are arranged at predetermined intervals in the right-left direction (see FIG. 2), but the configurations of the beads are limited thereto as long as a part of the workpiece W is formed into the stepped shape.

For example, as shown in FIG. 6, two flat beads 212 may be formed at a predetermined interval in the front-rear direction.

The bead 212 forms a rectangular shape as seen from above. The bead 212 protrudes upward from the top surface 10 a, and has a flat top surface. The bead 212 is continuously formed from the vicinity of the left end to the vicinity of the right end of the top surface 10 a of the lower die 10, and is continuously formed from the vicinity of one end to the vicinity of the middle of the top surface 10 a of the lower die 10 in the front-rear direction. The bead 212 is formed in order to change the top surface 10 a of the lower die 10 into a bumpy surface.

As show in FIG. 7, a plurality of semispherical beads 312 may be formed at predetermined intervals.

The bead 312 has a shape similar to that of one of two equal parts into which a sphere is divided, and is arranged so that the flat surface (cutting surface of one of two equal parts into which a sphere is divided) comes in contact with the top surface 10 a. Three beads 312 are arranged at predetermined intervals in the right-left direction, and additionally a plurality of sets of the three beads 312 are arranged at predetermined intervals in the front-rear direction. The bead 312 is formed in order to change the top surface 10 a of the lower die 10 into a bumpy surface.

In the present embodiment, the lower die 10 having the protrusion 11, and the upper die 20 having the recess 21 are used, but a lower die having a recess, and an upper die having a protrusion may be used.

In the present embodiment, the lower die 10 and the upper die 20 have shapes to form the workpiece W into the hat shape, but the shapes of the dies are not limited thereto. The dies may have other shapes.

INDUSTRIAL APPLICABILITY

The present invention is applied to a hot-pressing method and a hot-pressing apparatus for pressing and cooling a heated workpiece at the same time.

REFERENCE SIGNS LIST

1: hot-pressing apparatus

10: lower die

10 a: top surface

10 b: lateral surface

10 c: base surface

11: protrusion

12: bead

20: upper die

20 a: bottom surface

20 b: lateral surface

20 c: base surface

21: recess 

1. (canceled)
 2. A hot-pressing apparatus comprising a lower die having a lower forming surface, and an upper die having an upper forming surface facing the lower forming surface, which causes the lower die and the upper die to press a heated workpiece arranged therebetween, and at the same time, to keep the forming surfaces thereof in contact with a surface of the workpiece to cool the workpiece, wherein one of the lower die and the upper die has a protrusion which protrudes from an intermediate part, in a right-left direction, of the forming surface thereof toward the forming surface of the other, and which is continuously formed in a front-rear direction perpendicular to the right-left direction, the other of the lower die and the upper die has a recess which is recessed from an intermediate part, in the right-left direction, of the forming surface thereof in conformity with a shape of the protrusion, and which is continuously formed in the front-rear direction, the forming surface on which the protrusion is formed includes a top surface extending in the right-left direction at a protruding end of the protrusion, two lateral surfaces extending in a direction opposite to that in which the protrusion protrudes from both ends of the top surface in the right-left direction, and two base surfaces extending outward in the right-left direction from extending ends of the lateral surfaces, and the top surface is formed as a bumpy surface for forming a part of the workpiece corresponding to the top surface into a stepped shape when the upper die arrives at a vicinity of a bottom dead center.
 3. (canceled) 